excretion 2

Question 1

define and explain the importance of excretion

Answer 1

-excretion is a process by which metabolic waste products and toxic materials are removed from an organisms body
-the kidney filters out the waste products form the blood to prevent the accumulation of the waste products which may be toxic

Question 2

how does blood enter the kidney tubules

Answer 2

-blood enters the kidney through the renal artery which branches into many arterioles which further divide into mass of blood capillaries or the glomerulus
-blood leaves the renal corpuscle and enters tubule
-blood capillaries unite to form venules which join again to form renal vein where blood exits the kidney

Question 3

urine formation through glomerular filtration

Answer 3

-in the renal corpuscle, renal artery split up to numerous arterioles that enter the nephron, further dividing into capillaries which form the glomerulus that is surrounded by the bowman’s capsule
-afferent arteriole leading into the glomerulus is wider than the efferent arteriole bringing blood out, hence high hydrostatic blood pressure in capillaries of glomerulus that forces plasma out of the blood by ultrafiltration
-only blood cells, platelets and large plasma molecules remain in the blood due to basement membrane which allows water and small molecules to pass through
-filtrate is collected at the bowman’s capsule of renal corpuscle

Question 4

urine formation through selective reabsorption

Answer 4

-starts in the proximal convoluted tube
-almost 80 percent of filtrate in PCT is reabsorbed into blood to ensure all useful material is returned into the blood
-all glucose, AA and 85 percent of mineral ions are reabsorbed by AT into blood
-small proteins
-80 percent of water
-PCT have mitochondria to release energy required for the reabsorption of mineral ions through active transport and microvilli to increase SA for faster absorption

Question 5

where is water and salts reabsorbed

Answer 5

-water reabsorbed in PCT, LoH, DCT and CD
-salts reabsorbed in PCT and DCT

Question 6

how does glucose end up in urine

Answer 6

-AT mechanism has a maximum rate at which they can move substances, when this threshold is exceeded, AT cannot keep up with to reabsorb back all the glucose and hence ends up in urine

Question 7

what is pituitary glands and hypothalamus

Answer 7

-secretes ADH
-has receptors that detect changes in blood water potential

Question 8

osmoregulation, large intake of water, sweat

Answer 8

large intake of water increases water potential of plasma which stimulates the hypothalamus that instructs the pituitary glands to secrete less ADH so less water is reabsorbed in the kidney tubes, more diluted urine is excreted so water potential in plasma returns to normal

Question 9

how is blood cleaned in dialysis

Answer 9

-blood is drawn from an artery in the patients arm and is pumped through a tubing to dialysis machine
-tubing is bathed in special dialysis fluid which contains same concentration of essential substances in blood but no metabolic waste and the tubing is partially permeable
-small molecules like urea and metabolic waste products diffuse out of the tubing while larger molecules like platelets and blood cells remain in the tubing
-filtered blood returns to patients arm’s vein